This invention relates to a failure detection system for hydraulic pumps which are now widely in use to provide a source of hydraulic fluid for hydraulic machines and apparatus, including hydraulic excavators, cranes, etc.
A hydraulic pump is one of the most important elements of hydraulic excavators, cranes and other hydraulic machines and apparatus for producing hydraulic energy, and a deterioration of its performance due to a technical failure or a change occurring with time adversely affects the reliability in operation of a machine and apparatus for which it serves as a source of power. Thus, it is necessary to check the hydraulic pump for its performance. A system of the prior art for checking hydraulic pumps to detect their technical failures and a deterioration of performance (hereinafter referred to as failures) will be discussed.
A variable displacement type hydraulic pump which is to be monitored to detect its failure by the system of the prior art comprises displacement varying means (hereinafter referred to as a swash plate) and is connected to a regulator so as to operate the swash plate in accordance with its discharge pressure. The system of the prior art for detecting a failure of the hydraulic pump comprises a hydraulic pressure tester which comprises a pressure gauge for measuring the hydraulic pressure, a flowmeter for measuring the flow rate of a hydraulic fluid, and a manually operated variable throttle for throttling the discharge line of the variable displacement hydraulic pump to raise the dischage pressure. The variable displacement hydraulic pump is also connected to a device for measuring the rpm. of the pump.
To detect a failure of the variable displacement hydraulic pump, a line connected to the discharge side of the pump is cut off and the pump is connected at the discharge side to an inlet of the hydraulic pressure tester via a line, such as a hydraulic hose, while an outlet of the hydraulic pressure tester is connected to a hydraulic fluid reservoir via a line, such as a hydraulic hose. Then, the variable displacement hydraulic pump is driven by a prime mover, such as an engine, and the rpm. N of the pump is measured by the device for measuring the rpm. of the pump. While the pump is in this condition, the variable throttle of the hydraulic pressure tester is actuated to throttle the discharge line until the value of the pressure gauge (discharge pressure of the variable displacement hydraulic pump) becomes equal to a reference pressure P.sub.ref set beforehand. The discharged hydraulic fluid volume Q of the pump obtained at this time is measured by the flowmeter. In this case, the actual discharged hydraulic fluid volume is decided by the position of the swash plate which is controlled by the regulator in accordance with the discharge pressure of the pump. Then, a theoretical discharged hydraulic fluid volume Q.sub.ref is calculated based on the rpm. N and reference pressure P.sub.ref. Finally, the discharged hydraulic fluid volume Q measured beforehand is compared with the theoretical discharged hydraulic fluid volume Q.sub.ref, and when the difference between them exceeds an allowable value, the pump is found to be out of order.
The system for detecting a failure of a hydraulic pump of the prior art of the aforesaid construction has some disadvantages, although it is possible for it to detect a failure. In checking the pump, it is necessary to cut off a part of the hydraulic fluid piping and connect a hose and a hydraulic pressure tester to the pump. This operation is time-consuming, and there is the risk of dust and other foreign matter being incorporated in the hydraulic fluid in cutting off the piping. Checking the pump requires operation of the variable throttle and reading the pressure gauge and flow meter. This operation is also time-consuming and troublesome. Moreover, in the case of a hydraulic machine and apparatus, such as a hydraulic excavator of a large size, a multiplicity of hydraulic pumps are provided. In this case, it is time-consuming and troublesome to identify, when it is known that some of them are out of order but it is not known which ones have failed, the failed pumps.